Thread: Converter help

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Just installed a 383 from a 350 crate motor.
The truck weighs 2900 using a 670CFM whne the truck is in park it will idle at 1000 rpm....once I drop it in gear it wll drop to 400 rpm then stall out.
I assume I need a bigger converter but do I need 2000 or should I go higher.
Run on the street most of the time

I'd be thinkin' vacuum leak, assuming the valves are adjusted correctly. The motor shouldn't need 1000 rpm's to idle unless you have waaaaayyy overcammed it. What cam is in the motor? What's the ignition lead at the crank? What's the static compression ratio?

There are two possibilities for a vacuum leak, external and internal. With the motor idling, use a propane torch (not lit) and play the gas around the base of the carb and the intake manifold where it bolts to the heads. If the idle speed goes up, there is your external vacuum leak. You can't find an internal vacuum leak with gas. It's where the bottom of the intake manifold ports are open to the crankcase because the intake manifold ports and the cylinder head ports are not parallel and the motor draws in oily vapors when the intake valve is open. Have you checked the plugs for oily?

Well if it does need a converter I would go with a 3,000 to 3,800 stall but it all depends on your engine combo. I use to run a mild 351w with a 3,500 stall and my car weighs 3,000 without driver.

Originally Posted by iceburgh

Just installed a 383 from a 350 crate motor.
The truck weighs 2900 using a 670CFM whne the truck is in park it will idle at 1000 rpm....once I drop it in gear it wll drop to 400 rpm then stall out.
I assume I need a bigger converter but do I need 2000 or should I go higher.
Run on the street most of the time

Originally Posted by techinspector1

I'd be thinkin' vacuum leak, assuming the valves are adjusted correctly. The motor shouldn't need 1000 rpm's to idle unless you have waaaaayyy overcammed it. What cam is in the motor? What's the ignition lead at the crank? What's the static compression ratio?

There are two possibilities for a vacuum leak, external and internal. With the motor idling, use a propane torch (not lit) and play the gas around the base of the carb and the intake manifold where it bolts to the heads. If the idle speed goes up, there is your external vacuum leak. You can't find an internal vacuum leak with gas. It's where the bottom of the intake manifold ports are open to the crankcase because the intake manifold ports and the cylinder head ports are not parallel and the motor draws in oily vapors when the intake valve is open. Have you checked the plugs for oily?

hope I dont need a converter.
I did readjust the valves and it got much better but still not there
Here is the cam specs :288°/292° 224°/224° .450"/.460" 114°
32 degrees at 2000 but I also have the vacum advance where Holley says to hook it up ....but there is vacum there all the time even at idle.
How close are Holleys from the box.....could it be to rick or lean?

Vacuum leak or lean carb. With that cam and carb, a 383 should idle against a stock converter. I'd try a carb off a running engine, if that one works, you know where the trouble is. Beg, borrow, or steal one off a buddy.